The only other thing that I thought of is - was the kitty an outside
kitty before you adopted her? Maybe that made her coat extra thick
and thus all the shedding.

I adopted a Maine Coon from the shelter about 3 years ago and he eats
100 percent canned food - his shedding is not a big deal. A little at
this time of year and I comb him once a day, but I don't get more than
a teaspoon full out of him. I find a fine needled comb works better
than a brush at pulling out the loose hair.

If your kitty is nervous, that would also add to the shedding problem.